Two-component polyurethane adhesive

ABSTRACT

This invention relates to a low-viscosity two-component filled polyurethane adhesive comprising 
     (a) a low-viscosity isocyanate component in a quantity sufficient to provide an isocyanate index of about 100 to about 150 comprising an organic polyisocyanate in which up to 10 equivalent percent of the isocyanate groups have been modified by reaction with one or more isocyanate-reactive compounds; and 
     (b) a low-viscosity phase-stable curative component comprising 
     (i) 5 to 50 equivalent percent of a polyether polyol and/or a polyether terminated by aromatic amino groups having an equivalent weight greater than 500, 
     (ii) 30 to 95 equivalent percent of 2-methyl-1,3-propanediol, and 
     (iii) 0 to 35 equivalent percent of a chain extender and/or crosslinker other than 2-methyl-1,3-propanediol, with the proviso that the equivalent ratio of component (b)(iii) to component (b)(ii) is no more than about 0.6, 
     wherein at least one of components (a) or (b) contains 10 to 40 percent by weight, based on filled polyurethane adhesive, of at least one filler.

BACKGROUND OF THE INVENTION

The present invention relates to a low-viscosity two-component filledpolyurethane adhesive comprising an organic polyisocyanate component andan isocyanate-reactive curative component. The curative componentcomprises a phase-stable blend of a relatively high equivalent weightisocyanate-reactive polyether component with 2-methyl-1,3-propanedioland other optional chain extenders or crosslinkers, including lowmolecular weight diamines or triamines that impart sag resistance.

Urethane-based adhesives are known for use in joining together variousplastic materials. Although certain preformed polyurethanes can be usedas adhesives by applying heat (for example, U.S. Pat. No. 4,156,064),the preferred urethane adhesives are typically two-componenturethane-based adhesives comprised of an isocyanate component and anisocyanate-reactive curative component. Such adhesives are preferredover other adhesives, at least in part because of outstanding bondstrength, flexibility, and resistance to shock and fatigue.

Various approaches for preparing improved two-component urethaneadhesives have been described. One approach uses certain specialreagents to improve the properties of the adhesives. For example, theaddition of certain amide acetals to the curative component improvesadhesive properties by inhibiting foaming. E.g., U.S. Pat. No.4,728,710. The use of certain special isocyanate-reactive compounds (forexample, special amines, amino alcohols, and thiols) as part of thecurative component also provides improved adhesives. E.g., U.S. Pat.Nos. 3,714,127, 3,812,003, 3,935,051, and 4,336,298.

It is possible to improve adhesive properties without the need forspecial reagents of the types described above. For example, U.S. Pat.Nos. 3,979,364 and 4,743,672 disclose two-component urethane adhesivesin which the curative component contains mixtures of polyols andpolyoxyalkylene polyamines. These polyamines, in which the amino groupsare bound to aliphatic carbon atoms, impart sag resistance as well asimproved adhesion.

Efforts to improve adhesive properties have also focused on the polyolcomponent of the curative component. For example, U.S. Pat. No.4,336,298 specifically requires the use of polyester or polyether triolshaving a molecular weight range of about 400 to 1000, which correspondsto an equivalent weight of no more than about 333. U.S. Pat. No.4,444,976 specifies a curative component containing polyols having atleast two hydroxyl groups and a molecular weight range of about 100 to2000, which corresponds to an equivalent weight of no more than 1000.Higher molecular weight polyols are disclosed but only for thepreparation of prepolymers used as the polyisocyanate component. U.S.Pat. No. 4,552,934 discloses a curative component containing hydroxylterminated prepolymers prepared by the reaction of organicpolyisocyanates, polyols having a molecular weight range of about 150 to3000, and polyamines. European Patent Application 304,083 discloses anisocyanate component containing a blend of an aliphatic isocyanate andan aromatic isocyanate prepolymer and a curative component containing apolyfunctional polyether polyol having a hydroxyl number of from 100 to1200 (corresponding to equivalent weights of about 45 to about 561), adiamine, and an optional catalyst. Higher molecular weight polyols aredisclosed but only for the preparation of the prepolymers of theisocyanate component.

Japanese Patent 89/48,876 discloses a two-component urethane adhesivehaving a polyisocyanate component and a curative component containing amixture of relatively high molecular weight polyols, relatively lowmolecular weight polyols, zeolite filler, and catalyst. The patent,however, does not disclose any special role for2-methyl-1,3-propanediol.

European Patent Application 328,808 discloses a two-component urethaneadhesive having an isocyanate-terminated urethane prepolymer componentand a curative component containing a nitrogen-free polyol (preferably alow molecular weight diol) and a primary amine for sag resistance, aswell as optional fillers and other additives. In contrast to the presentinvention, the European application does not suggest the importance ofusing a curative component containing both relatively high equivalentweight polyether polyols and 2-methyl-1,3-propanediol or other lowmolecular weight diol chain extenders or crosslinkers.

The use of low viscosity components in two-component adhesive systems isdesirable as long as sag is not excessive. U.S. Pat. No. 4,552,934describes the desirability of low viscosity components havingviscosities of 35,000 cps (i.e., 35,000 mPa.s) for the isocyanatecomponent and approximately 50,000 cps for the curative component.Although described as having low viscosities, both adhesive componentsof the patent are considerably more viscous than those of the presentinvention. U.S. Pat. No. 4,336,298 discloses a low viscosity hardenercomponent having a viscosity of from 400 to 8000 mPa.s but requires ahigher viscosity isocyanate component having a viscosity of from 20,000to 55,000 mPa.s.

Two-component adhesives based on isocyanate-reactive curative blendscontaining relatively high equivalent weight isocyanate-reactivepolyethers, low molecular weight diol chain extenders or crosslinkers,and amine have been disclosed. E.g., U.S. Pat. Nos. 4,994,540,5,164,473, and 5,204,439. However, the curative components of suchadhesives have typically been unstable with respect to separation intophases.

It has now surprisingly been found that isocyanate-reactive curativeblends containing a relatively high equivalent weight polyethercomponent, 2-methyl-1,3-propanediol, and optional chain extenders and/orcrosslinkers other than 2-methyl-1,3-propanediol are stable to phaseseparation while still exhibiting low viscosity. Such blends, when usedwith a low viscosity polyisocyanate component, provide two-componentadhesives having advantageous properties. For example, adhesivesaccording to the invention, although used without primer, exhibitexcellent high temperature bonding strength. When low molecular weightisocyanate-reactive diamines or triamines am used as chain extenders orcrosslinkers, the mixed adhesives of the invention exhibit excellentresistance to flow, or "sag", despite the fact that both reactivecomponents are characterized by low viscosities of less than about15,000 mPa.s.

Although some of the compositions described as useful in the abovereferences can also be used with the present invention, none of thereferences discloses or suggests the combinations of components that arecritical to this invention. In particular, none discloses the use of acurative component containing mixtures of a relatively high equivalentweight isocyanate-reactive polyether and 2-methyl-1,3-propanediol (andother optional low equivalent weight chain extenders or crosslinkers)that are stable to phase separation.

SUMMARY OF THE INVENTION

The present invention relates to a low-viscosity two-component filledpolyurethane adhesive having a urethane content of from 7 to 20 percentby weight (preferably 9 to 17 percent by weight and more preferably 10to 14 percent by weight), based on the weight of nonfilled polyurethanepolymer, comprising

(a) a low-viscosity isocyanate component in a quantity sufficient toprovide an isocyanate index of about 100 to about 150 (preferably 115 to140) comprising an organic polyisocyanate wherein 0 to 10 equivalentpercent (preferably up to 5 equivalent percent) of the isocyanate groupsof said organic polyisocyanate have been modified by reaction with oneor more isocyanate-reactive compounds; and

(b) a low-viscosity curative component that is resistant to phaseseparation comprising

(i) about 5 to about 50 equivalent percent (preferably 5 to 20equivalent percent), based on the total equivalents of amino andhydroxyl groups of component (b), of an isocyanate-reactive polyetherhaving an equivalent weight greater than 500 (preferably 500 to 20,000and more preferably 1000 to 10,000) selected from the group consistingof polyether polyols, polyethers terminated by aromatic amino groups,and mixtures thereof,

(ii) about 30 to about 95 equivalent percent (preferably 70 to 95equivalent percent), based on the total equivalents of amino andhydroxyl groups of component (b), of 2-methyl-1,3-propanediol, and

(iii) 0 to about 35 equivalent percent (preferably 0.5 to 17 equivalentpercent and more preferably 6 to 12 equivalent percent), based on thetotal equivalents of amino and hydroxyl groups of component (b), of oneor more chain extenders and/or crosslinkers other than2-methyl-1,3-propanediol having a molecular weight in the range of 32 to400 (preferably a mixture of chain extenders and/or crosslinkerscontaining one or more isocyanate-reactive diamines or triamines havinga molecular weight in the range of about 62 to 400 in a quantitysufficient to produce resistance to flow when components (a) and (b) aremixed), with the proviso that the equivalent ratio of component (b)(iii)to component (b)(ii) is no more than about 0.6 (preferably no more thanabout 0.5 and more preferably no more than about 0.35),

wherein at least one of components (a) or (b) contains at least onefiller in a quantity of from about 10 to about 40 percent by weightbased on the total quantity of filled polyurethane adhesive.

DETAILED DESCRIPTION OF THE INVENTION

The isocyanate component (a) comprises an organic polyisocyanate inwhich part of the isocyanate groups can be modified by reaction with oneor more isocyanate-reactive compounds. Suitable polyisocyanates includealiphatic, cycloaliphatic, araliphatic, aromatic, and heterocyclicpolyisocyanates of the type described, for example, by W. Siefken inJustus Liebigs Annalen der Chemie, 562, pages 75 to 136. Suchisocyanates include those having the formula

    Q(NCO).sub.n

in which n is a number from 2 to about 5 (preferably 2 to 3) and Q is analiphatic hydrocarbon group containing 2 to about 18 (preferably 6 to10) carbon atoms, a cycloaliphatic hydrocarbon group containing 4 toabout 15 (preferably 5 to 10) carbon atoms, an araliphatic hydrocarbongroup containing 8 to 15 (preferably 8 to 13) carbon atoms, or anaromatic hydrocarbon group containing 6 to about 15 (preferably 6 to 13)carbon atoms. Examples of suitable polyisocyanates include ethylenediisocyanate; 1,4-tetramethylene diisocyanate; 1,6-hexamethylenediisocyanate; 1,12-dodecamethylene diisocyanate;cyclobutane-1,3-diisocyanate; cyclohexane-1,3- and -1,4-diisocyanate,and mixtures of these isomers;1-isocyanato-2-isocyanatomethylcyclopentane; 1-isocyanato-1-methyl-3-and/or -4-isocyanatomethylcyclohexane ("IMCI"); 1,3- and1,4-bis(isocyanatomethyl)cyclohexane;1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane ("isophoronediisocyanate" or "IPDI"; see, e.g., German Auslegeschrift 1,202,785 andU.S. Pat. No. 3,401,190); 2,4- and 2,6-hexahydrotolylene diisocyanateand mixtures of these isomers; dicyclohexylmethane-4,4'-diisocyanate("hydrogenated MDI" or "HMDI"), including the t,t-, c,t-, andc,c-isomers thereof; dicyclohexylmethane-2,4'-diisocyanate;α,α,α',α'-tetramethyl-1,3- and/or -1,4-xylylene diisocyanate ("TMXDI");1,3- and 1,4-phenylene diisocyanate; 2,4- and 2,6-toluene diisocyanateand mixtures of these isomers ("TDI"); diphenylmethane-2,4'- and/or-4,4'-diisocyanate ("MDI"); naphthylene-1,5-diisocyanate;triphenylmethane-4,4',4"-triisocyanate;polyphenyl-polymethylenepolyisocyanates of the type which may beobtained by condensing aniline with formaldehyde, followed byphosgenation ("crude MDI"), which are described, for example, in BritishPatents 878,430 and 848,671; norbornane diisocyanates, such as describedin U.S. Pat. No. 3,492,330; m- and p-isocyanatophenylsulfonylisocyanates of the type described in U.S. Pat. No. 3,454,606;and perchlorinated aryl polyisocyanates of the type described, forexample, in U.S. Pat. No. 3,227,138. It is also possible to use theisocyanate-containing distillation residues accumulating in theproduction of isocyanates on a commercial scale, optionally in solutionin one or more other polyisocyanates.

Suitable modified polyisocyanates can be prepared by the reaction oforganic polyisocyanates such as described above with one or morecompounds containing isocyanate-reactive groups, such as hydroxyl,amino, and thiol groups (preferably hydroxyl and/or amino groups) andhaving a functionality of about 2 to about 6 and an equivalent weightgreater than about 500, such that up to about 10 (preferably up to 5)equivalent percent of the isocyanate groups have been modified.Preferred isocyanate-reactive compounds have a functionality of about 2to about 6 and an equivalent weight greater than about 500. Examples ofsuitable modified polyisocyanates include modified polyisocyanatescontaining urethane groups of the type described, for example, in U.S.Pat. Nos. 3,394,164 and 3,644,457; modified polyisocyanates containingallophanate groups of the type described, for example, in British Patent994,890, Belgian Patent 761,616, and published Dutch Patent Application7,102,524; modified polyisocyanates containing isocyanurate groups ofthe type described, for example, in U.S. Pat. No. 3,002,973, GermanPatentschriften 1,022,789, 1,222,067 and 1,027,394, and GermanOffenlegungsschriften 1,919,034 and 2,004,048; modified polyisocyanatescontaining urea groups of the type described in German Patentschrift1,230,778; polyisocyanates containing biuret groups of the typedescribed, for example, in German Patentschrift 1,101,394, U.S. Pat.Nos. 3,124,605 and 3,201,372, and in British Patent 889,050; andmodified polyisocyanates containing carbodiimide groups of the typedescribed in U.S. Pat. No. 3,152,162. It is also possible to usemixtures of the polyisocyanates described above.

Preferred organic polyisocyanates of the isocyanate component (a) arethose based on MDI or HMDI. Examples of preferred MDI-basedpolyisocyanates include (i) mixtures of diphenylmethane-2,4'- and/or-4,4'-diisocyanate isomers (preferably having a 2,4'-isomer content ofabout 5 to about 40 and most preferably 10 to 25 percent by weight),optionally in admixture with polyphenyl polymethylene polyisocyanates,wherein the diphenylmethane diisocyanate isomers comprise from about 20to 100 percent by weight of the total polyisocyanate mixture; (ii)urethane- and/or urea-modified MDI-based di- and/or polyisocyanates inwhich no more than about 10 (preferably no more than 5) equivalentpercent of the isocyanate groups have been modified by reaction with oneor more isocyanate-reactive hydroxyl- and/or amino-containing compounds,wherein said isocyanate-reactive compounds have a functionality of about2 to about 6 and an equivalent weight greater than about 500 (preferably500 to 20,000); and (iii) dicyclohexylmethane-2,4'- and/or-4,4'-diisocyanate, preferably the 4,4'-isomer.

Suitable polyether polyols for use in component (b)(i) includepolyethers prepared, for example, by the polymerization of epoxides suchas ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran,styrene oxide, or epichlorohydrin, optionally in the presence of Lewisacids such as BF₃, or prepared by chemical addition of such epoxides,optionally added as mixtures or in sequence, to starting componentscontaining reactive hydrogen atoms, such as water, alcohols, or amines.Examples of starting components include ethylene glycol, 1,3- or1,2-propanediol, 1,2-, 1,3-, or 1,4-butanediol, trimethylolpropane,4,4'-dihydroxydiphenylpropane, aniline, ammonia, ethanolamine, orethylene diamine. Sucrose polyethers of the type described, for example,in German Auslegeschriften 1,176,358 and 1,064,938 may also be usedaccording to the invention. Polyethers which contain predominantlyprimary hydroxyl groups (up to about 90% by weight, based on all of thehydroxyl groups in the polyether) are also suitable. Polyethers modifiedby vinyl polymers of the kind obtained, for example, by thepolymerization of styrene and acrylonitrile in the presence ofpolyethers (e.g., U.S. Pat. Nos. 3,383,351, 3,304,273, 3,523,093, and3,110,695 and German Patent 1,152,536) are also suitable, as arepolybutadienes containing hydroxyl groups. Particularly preferredpolyether polyols include polyoxyalkylene polyether polyols, such aspolyoxyethylene diol, polyoxypropylene diol, polyoxybutylene diol, andpolytetramethylene diol, as well as polyoxypropylene polyoxyethylenetriols.

Other suitable polyol polyethers for use in component (b)(i) include theso-called PHD polyols, which are prepared by reactions of organicpolyisocyanates, hydrazine, and polyether polyols. U.S. Pat. No.3,325,421 discloses a method for producing suitable PHD polyols byreacting a stoichiometric or substoichiometric quantity (relative todiamine) of polyisocyanate dissolved in a polyol having a molecularweight of at least 500 and a hydroxyl number of no more than 225. Seealso U.S. Pat. Nos. 4,042,537 and 4,089,835.

Suitable polyol polyethers for use in component (b)(i) also include theso-called polymer polyols, which are prepared by polymerizing styreneand acrylonitrile in the presence of a polyether. See, for example, U.S.Pat. Nos. 3,383,351, 3,304,273, 3,523,093, 3,652,639, 3,823,201, and4,390,645.

Also suitable are so-called amine-terminated polyethers containingaromatically and/or aliphatically (preferably aromatically) boundisocyanate-reactive primary or secondary (preferably primary) aminogroups. Compounds containing amino end groups can also be attached tothe polyether chain through urethane or ester groups. Theseamine-terminated polyethers can be prepared by any of several methodsknown in the art. For example, amine-terminated polyethers can beprepared from polyhydroxyl polyethers (e.g., polypropylene glycolethers) by a reaction with ammonia in the presence of Raney nickel andhydrogen (Belgian Patent 634,741). Polyoxyalkylene polyamines can beprepared by a reaction of the corresponding polyol with ammonia andhydrogen in the presence of a nickel, copper, chromium catalyst (U.S.Pat. No. 3,654,370). The preparation of polyethers containing amino endgroups by the hydrogenation of cyanoethylated polyoxypropylene ethers isdescribed in German Patentschrift 1,193,671. Other methods for thepreparation of polyoxyalkylene (polyether) amines are described in U.S.Pat. Nos. 3,155,728 and 3,236,895 and in French Patent 1,551,605. FrenchPatent 1,466,708 discloses the preparation of polyethers containingsecondary amino end groups. Also useful are the polyether polyaminesdescribed in U.S. Pat. Nos. 4,396,729, 4,433,067, 4,444,910, and4,530,941.

In one method for preparing aromatic amine-terminated polyethers,relatively high molecular weight polyhydroxy-polyethers suitable for theprocess of the present invention may be converted into the correspondinganthranilic acid esters by reaction with isatoic acid anhydride. Methodsfor making polyethers containing aromatic amino end groups are disclosedin German Offenlegungsschriften 2,019,432 and 2,619,840 and U.S. Pat.Nos. 3,808,250, 3,975,428, and 4,016,143. Relatively high molecularweight compounds containing amino end groups may also be obtainedaccording to German Offenlegungsschrift 2,546,536 or U.S. Pat. No.3,865,791 by reacting isocyanate prepolymers based on polyhydroxylpolyethers with hydroxyl-containing enamines, aldimines, or ketiminesand hydrolyzing the reaction product.

Preferred aromatic amine-terminated polyethers include amino-polyethersobtained by the hydrolysis of compounds containing isocyanate endgroups. For example, in a process disclosed in GermanOffenlegungsschrift 2,948,419, polyethers containing hydroxyl groups(preferably two or three hydroxyl groups) react with polyisocyanates toform isocyanate prepolymers, the isocyanate groups of which are thenhydrolyzed in a second step to amino groups. Preferred amine-terminatedpolyethers are prepared by hydrolyzing aromatic isocyanate compoundshaving an isocyanate group content of from 0.5 to 40% by weight. Themost preferred such polyethers are prepared by first reacting apolyether containing two to four hydroxyl groups with an excess of anaromatic polyisocyanate to form an isocyanate terminated prepolymer andthen converting the isocyanate groups to amino groups by hydrolysis.Processes for the production of useful amine-terminated polyethers usingisocyanate hydrolysis techniques are described in U.S. Pat. Nos.4,386,218, 4,456,730, 4,472,568, 4,501,873, 4,515,923, 4,525,534,4,540,720, 4,578,500, and 4,565,645; European Patent Application 97,299;and German Offenlegungsschrift 2,948,419, all the disclosures of whichare herein incorporated by reference. Similar products are alsodescribed in U.S. Pat. Nos. 4,506,039, 4,525,590, 4,532,266, 4,532,317,4,723,032, 4,724,252, 4,855,504, 4,931,595, and 5,283,364.

Other suitable amine-terminated polyethers includeaminophenoxy-substituted polyethers described, for example, in EuropeanPatent Applications 288,825 and 268,849.

Aminocrotonate-terminated derivatives of polyethers, as well as of otherpolyols described above, can be prepared from acetoacetate-modifiedpolyethers as described, for example, in U.S. Pat. Nos. 5,066,824,5,151,470, 5,231,217, and 5,356,946.

The amine-terminated polyethers can often be used as mixtures withpolyols and other amine-terminated compounds. Such mixtures shouldpreferably contain (on a statistical average) two to threeisocyanate-reactive amino end groups.

Preferred compounds for use in component (b)(i) are polyether polyols,the so-called PHD polyols, polyethers terminated with aromatic aminogroups, and mixtures thereof. The most preferred compounds for use incomponent (b)(i) include (a) polyoxypropylene polyoxyethylene triolshaving an equivalent weight greater than about 500 (preferably greaterthan 1000) and/or (b) amine-terminated polyethers prepared by firstreacting a polyether containing two to four hydroxyl groups (preferablya polyoxypropylene polyoxyethylene triol having an equivalent weightgreater than about 1000) with an excess of an aromatic polyisocyanate(preferably toluene diisocyanate) to form an isocyanate-terminatedprepolymer and then hydrolyzing the isocyanate groups of theisocyanate-terminated prepolymer to form the amine-terminated polyether.

Component (b)(ii) must be 2-methyl-1,3-propanediol but can optionally beused in admixture with up to about 0.6 equivalents (preferably up toabout 0.5 equivalents and more preferably up to about 0.35 equivalents),per equivalent of 2-methyl-1,3-propanediol, of one or more other chainextenders (i.e., other than 2-methyl-1,3-propanediol) and/orcrosslinkers (b)(iii). The quantity of such other chain extenders and/orcrosslinkers is, however, somewhat dependent on the composition ofisocyanate-reactive polyether (b)(i). Suitable chain extenders andcrosslinkers (b)(iii) contain at least two hydroxyl groups and/orprimary or secondary amino groups and have molecular weights of 32 to400. In general, chain extenders are difunctional isocyanate-reactivecompounds, whereas crosslinkers are trifunctional or higherfunctionality isocyanate-reactive compounds. Suitable chain extendersand/or crosslinkers, if used at all, can contain hydroxyl groups as theonly isocyanate-reactive groups. Examples of suitablehydroxyl-containing chain extenders and crosslinkers include ethyleneglycol, 1,2- and 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol,glycerol, trimethylolpropane, pentaerythritol, quinitol, mannitol,diethylene glycol, triethylene glycol, tetraethylene glycol, dipropyleneglycol, dibutylene glycol. Particularly preferred hydroxyl-containingchain extenders are diols such as ethylene glycol, 1,2-propanediol, and1,4-butanediol. It is also possible to use chain extenders containingboth hydroxyl and amino groups, such as diethanolamine anddiisopropanolamine. Mixtures containing more than one chain extenderand/or crosslinker can, of course, also be used in admixture with the2-methyl-1,3-propanediol.

Particularly useful adhesives exhibit resistance to flow when components(a) and (b) are mixed. Suitable flow resistance can be achieved byincluding in component (b)(iii) as little as 0.5 equivalent percent(based on the total equivalents of amino and hydroxyl groups ofcomponent (b)) of an isocyanate-reactive amine. Suitableisocyanate-reactive amines include aliphatic, cycloaliphatic, oraromatic diamines or triamines having a molecular weight in the range ofabout 62 to 400. Although substantially any isocyanate-reactive diamineor triamine can be used, preferred isocyanate-reactive amines arealiphatic or cycloaliphatic diamines having only primary amino groups,particularly ethylenediamine, hexamethylenediamine,bis(4-aminocyclohexyl)methane, and1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane ("IPDA"). A mostpreferred diamine is 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane.Known aromatic diamines are also suitable but are less preferred.Suitable but generally less preferred isocyanate-reactive amines containboth hydroxyl and amino groups. Mixtures of such amines are, of course,also suitable.

Thiol-containing chain extenders and/or crosslinkers, although possiblein principle, are much less preferred for use in component (b)(iii).

The isocyanate-reactive compounds of component (b) of the invention aredescribed in terms of equivalent weight, which can be calculated fromexperimentally determined hydroxyl numbers (and/or similarly determinedamine numbers) of a particular component using the well-knownrelationship described by the formula ##EQU1##

The corresponding molecular weight of a particular component can, ofcourse, be determined by multiplying the equivalent weight by thefunctionality of the component. A critical feature of the invention isthe use of a blend of a relatively high equivalent weightisocyanate-reactive component (b)(i) with 2-methyl-1,3-propanediol(b)(ii), as well as optional chain extenders and/or crosslinkers(b)(iii), to obtain a curative blend that is stable to phase separation("phase stable") and provides adhesives exhibiting excellent hightemperature bonding strength, as well as resistance to sag when suitablediamines or triamines are included.

The relative quantities of the individual compounds of component (b) areselected in such a way that the isocyanate-reactive groups of component(b)(i) comprise about 5 to about 50 equivalent percent (preferably 5 to20 equivalent percent), the hydroxyl groups of 2-methyl-1,3-propanediol(b)(ii) comprise about 30 to about 95 equivalent percent (preferably 70to 95 equivalent percent), and the isocyanate-reactive groups ofoptional component (b)(iii) comprise up to about 35 equivalent percent(preferably 0.5 to 17 equivalent percent and more preferably 6 to 12equivalent percent) of the total equivalents of amino and hydroxylgroups of component (b). The maximum amount of component (b)(iii) thatcan be blended with 2-methyl-1,3-propanediol (b)(ii) and still givephase-stable mixtures is somewhat dependent on the composition ofpolyether (b)(i) with which it is used. In general, however,phase-stable mixtures can contain up to about 0.6 equivalents(preferably up to about 0.5 equivalents and more preferably up to about0.35 equivalents) of other chain extenders or crosslinker per equivalentof 2-methyl-1,3-propanediol.

When included to provide flow resistance, isocyanate-reactive diaminesand triamines are used as all or a part of component (b)(iii) in amountsthat are at least sufficient to produce adequate resistance to flow whencomponents (a) and (b) are mixed. In general, the amount of the diamineand/or triamine is selected to provide 0.5 to 20 equivalent percent(more preferably 1 to 12 equivalent percent) of the totalisocyanate-reactive groups of component (b). It is possible forcomponent (b)(iii) to consist entirely of such isocyanate-reactivediamines and/or triamines as long as component (b) contains no more thanabout 15 equivalent percent (preferably 6 to 12 equivalent percent) ofsuch amines.

Suitable fillers include silicate-containing minerals, such asantigorite, serpentine, hornblends, amphiboles, chrysotile, talc, mica,and kieselguhr; metal oxides such as kaolin, aluminum oxides, titaniumoxides, and iron oxides; metal salts such as chalk and heavy spar(barium sulfate); inorganic pigments such as cadmium sulfide and zincsulfide; and glass, asbestos powder, carbon fibers, and the like.Preferred fillers are substantially inert under the conditionsencountered when the components of the invention are mixed. Aparticularly preferred filler is talc. Fillers may be used eitherindividually or in admixture. The fillers are added to either or both ofcomponents (a) and (b) in quantities totaling about 10 to about 40percent by weight based on the total quantity of the filled polyurethaneadhesive.

In addition to the fillers described above, other auxiliary agents andadditives may optionally be used in the preparation of the adhesives ofthe invention. Suitable auxiliary agents and additives may include, forexample, catalysts for the polyisocyanate-polyaddition reaction, dryingagents, surface-active additives, anti-foaming agents, pigments, dyes,UV stabilizers, plasticizers, and fungistatic or bacteriostaticsubstances, such as those described in European Patent Application81,701 at column 6, line 40, to column 9, line 31.

Both the isocyanate component and the curative component of the presentinvention are characterized by low viscosities, a characteristic thatfacilitates bulk handling. As used herein, the term "low viscosity"refers to a Brookfield viscosity at 25° C. of less than about 15,000mPa.s. Each component used in the present invention is characterized byviscosities at 25° C. of less than 15,000 mPa.s. Despite the use of suchlow viscosity components, the mixed adhesive exhibits excellentresistance to sag when diamines and/or triamines are present incomponent (b)(iii).

In the practice of the invention, the organic isocyanate component ismixed with the curative isocyanate-reactive component in a predeterminedratio designed to provide an isocyanate index of from about 100 to about150. The term "isocyanate index" is defined as the quotient, multipliedby 100, of the number of isocyanate groups divided by the number ofisocyanate-reactive groups. The filler, as well as the optionaladditives and auxiliaries, can be mixed with either or both of theisocyanate component and the isocyanate-reactive component but ispreferably mixed with both components. The components may be mixed byany of various known methods, including impingement mixing and staticmixing, and they may be applied to the substrate to be bonded as thinfilms or in the form of beads.

Adhesives prepared according to the invention, although used withoutprimer, exhibit excellent high temperature bonding strength, as measuredby the tests described in the examples. Furthermore, the curativecomponent of the invention is particularly resistant to phaseseparation, whereas polyol blends containing diols other than2-methyl-1,3-prepanediol are subject to separation. In addition,adhesives according to the invention produce improved high temperaturebonding properties when compared with adhesives based on polyol blendscontaining intermediate equivalent weight polyols instead of mixtures ofhigh equivalent weight polyols and 2-methyl-1,3-propanediol according tothe invention.

The following examples further illustrate details for the preparationand use of the compositions of this invention. The invention, which isset forth in the foregoing disclosure, is not to be limited either inspirit or scope by these examples. Those skilled in the art will readilyunderstand that known variations of the conditions and processes of thefollowing preparative procedures can be used to prepare thesecompositions. Unless otherwise noted, all temperatures are degreesCelsius and all percentages are percentages by weight.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following isocyanate-reactive compounds were used to prepare polyolblends used in the examples:

Polyether A A poly(propylene oxide) triol capped with ethylene oxide(equivalent weight 2000) (available as MULTRANOL® 9139 from BayerCorporation)

Polyether B An aromatic amine-terminated polyether (equivalent weight1833) prepared by the hydrolysis of the corresponding aromaticisocyanate-terminated polyether polyol

Polyether C A poly(propylene oxide) diol (equivalent weight 1000)

Extender A 2-Methyl-1,3-propanediol

Extender B 1,4-Butanediol

Extender C Bis(4-aminocyclohexyl)methane

Extender D 1-Amino-3,3,5-trimethyl-5-aminomethylcyclohexane (IPDA)

Extender E Ethylenediamine-started poly(propylene oxide) tetraol (i.e.,a crosslinker) (equivalent weight 89) (available as MULTRANOL® 4050 fromBayer Corporation)

Extender F Amine-terminated polyether (equivalent weight 200) (availableas JEFFAMINE® D-400 from Huntsman)

Extender G Ethylene glycol (1,2-ethanediol)

Extender H Propylene glycol (1,2-propanediol)

Extender I 1,6-Hexanediol

EXAMPLES 1-5

Adhesive performance

The polyisocyanate used to prepare the adhesives of Examples 1-5 was aurethane-modified polyisocyanate having an NCO content of about 27%prepared by the reaction of 71.5 parts of a polymeric diphenylmethanediisocyanate (2,4'-isomer content of about 19% and NCO functionality ofabout 2.4) with 13.8 parts of polyether A. Talc (36.5 parts) was blendedwith the modified polyisocyanate to yield a composition with anisocyanate content of 18.2% and a viscosity of 8400 mPa.s at 25° C.

Adhesive formulations were prepared using the above polyisocyanate andpolyol formulations at an isocyanate index of 128. The resultantadhesives were tested for performance using the lap shear (SAE J1525)test. Test results are shown in Table 1.

Lap Shear Procedure

Sheets of commercial grades of fiber-reinforced plastic ("FRP") (4 in.×9in.×0.125 in., or about 10 cm×23 cm×0.32 cm) were bonded together usingmetal spacers to insure a bond thickness of 0.030 inch (about 0.76 mm)and an overlap length of 1 inch (about 2.5 cm). The surface of the FRPwas wiped with a dry cloth prior to bonding to remove dust. No othersurface preparation was used. Samples prepared using the adhesives ofExamples 1-5 were cured in an oven for 60 minutes at 135° C. Attempts tocure additional samples prepared using the adhesive of Examples 4 and 5were made by curing in a heated clamp for 90 seconds at 135° C. and thenpostcuring for 30 minutes at 120° C. The adhesive of Example 4 cured asexpected but the adhesive of Example 5 showed no green strength and didnot cure sufficiently for testing purposes. Test specimens (1 inch, or2.5 cm, wide) were cut from the cured samples using a diamond tippedsaw. Samples were tested at a temperature of 82° C. after conditioning,for one hour at 82° C.

EXAMPLE 1

A polyol blend according to the invention was prepared from 71.5 partsof polyether A, 14.7 parts of polyether B, 17.5 parts of2-methyl-1,3-propanediol (i.e., Extender A), 3.5 parts ofbis(4-aminocyclohexyl)methane (i.e., Extender C), 13.3 parts of sodiumpotassium aluminosilicate in castor oil, 34 parts of talc, and 0.02parts of dimethyltin dilaurate catalyst. The polyol blend had aviscosity of 13,400 mPa.s at 25° C. and an equivalent weight of 318.

EXAMPLE 2

(comparison to Example 1)

A comparison polyol blend was prepared according to the method ofExample 1 except that 17.5 parts of 1,4-butanediol (i.e., Extender B)were used instead of 2-methyl-1,3-propanediol. The polyol blend had aviscosity of 12,100 mPa.s at 25° C. and an equivalent weight of 318.

EXAMPLE 3

A polyol blend according to the invention was prepared from 71.5 partsof polyether A, 17.5 parts of 2-methyl-1,3-propanediol (i.e., ExtenderA), 3.0 parts of IPDA (i.e., Extender D), 1.0 part of Extender E, 0.8parts of Extender F, 13.3 parts of sodium potassium aluminosilicate incastor oil, 34 parts of talc, and 0.02 parts of dimethyltin dilauratecatalyst. The polyol blend had an equivalent weight of 285.

EXAMPLE 4

(comparison to Example 3)

A comparison polyol blend was prepared according to the method ofExample 3 except that 14.8 parts of propylene glycol (i.e., Extender H)were used instead of 2-methyl-1,3-propanediol and Extender F wasomitted. The polyol blend had an equivalent weight of 280.

EXAMPLE 5

(comparison to Example 3)

A comparison polyol blend was prepared according to the method ofExample 3 except that 12.1 parts of ethylene glycol (i.e., Extender G)were used instead of 2-methyl-1,3-propanediol and Extender F wasomitted. The polyol blend had an equivalent weight of 275.

                  TABLE 1                                                         ______________________________________                                        Adhesive performance for Examples 1-5                                                           82° C. Lap Shear                                              Urethane              Fiber tear                                     Example  content (%)    MPa    (%)                                            ______________________________________                                        1        12.2           3.19   100                                            2 (comp) 12.2           3,00   100                                            3        13.3           4.08   100                                            4        13.6           3.06   100                                            5        13.8           2.25   7                                              ______________________________________                                    

The adhesion data show that excellent adhesion character was obtainedusing phase-stable polyol blends based on 2-methyl-1,3-propanediol(i.e., Examples 1 and 3) as well as the phase-unstable blends containingno 2-methyl-1,3-propanediol (i.e., comparison Examples 2 and 4).However, poor adhesion at elevated temperatures was observed for thephase-unstable blend of comparison Example 5. These data show that phasestability is not predictive of adhesive performance.

EXAMPLES 6-10 Phase stability evaluations

A series of polyol blends were prepared to determine the relative phasestabilities of blends containing various ratios of2-methyl-1,3-propanediol and various other alkanediols. The polyolblends used for Examples 6-10 did not contain the talc filler and otherblend components that were used for the polyol blends of Examples 1-5.Phase stability was determined by room temperature appearance (Example6-8) and by cloud point measurements (Examples 9 and 10), which allow anumerical valuation of degree of phase stability.

Comparison tests were conducted by using an equivalent ratio of extenderto 2-methyl-1,3-propanediol greater than 0.6 (i.e., comparison Examples7b, 7c, 8b, 9b, 9c, 10b, and 10c) or by omitting2-methyl-1,3-propanediol altogether (i.e., comparison Examples 6a, 7a,7g, 7h, 7i, 8a, 9a, 9f, 9g, 9h, and 10a).

Appearance tests

Phase stabilities determined by appearance at room temperature arereported using the following scale:

(1) Clear and homogeneous

(2) Cloudy and homogeneous

(3) Formation of two layers

(4) Solid/liquid mixture

Formulations and results are shown in Tables 2-4. Quantities are givenin parts by weight.

                  TABLE 2                                                         ______________________________________                                                        Example                                                                         6a                                                          Components        (comp)  6b                                                  ______________________________________                                        Polyether A       71.5    71.5                                                Polyether B       14.7    14.7                                                Extender A        --      17.5                                                Extender B        17.5    --                                                  Equiv. ratio      --      0                                                   Ext. B/Ext. A                                                                 Appearance                                                                    1 day             2       1                                                   14 days           3       1                                                   ______________________________________                                    

                                      TABLE 3                                     __________________________________________________________________________           Example                                                                       7a  7b  7c              7g  7h  7i                                     Components                                                                           (comp)                                                                            (comp)                                                                            (comp)                                                                            7d  7e  7f  (comp)                                                                            (comp)                                                                            (comp)                                 __________________________________________________________________________    Polyether A                                                                          71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                   Extender A                                                                           --  4.5 8.75                                                                              13  16.5                                                                              17.5                                                                              --  --  --                                     Extender B                                                                           17.5                                                                              13  8.75                                                                              4.5 1   --  --  --  --                                     Extender G                                                                           --  --  --  --  --  --  17.5                                                                              --  --                                     Extender H                                                                           --  --  --  --  --  --  --  17.5                                                                              --                                     Extender I                                                                           --  --  --  --  --  --  --  --  17.5                                   Equiv. ratio.sup.(1)                                                                 --  2.9 1.0 0.35                                                                              0.06                                                                              0   --  --  --                                     Ext. X/Ext. A                                                                 Appearance                                                                    1 day  2   2   2   1   1   1   2   1   4                                      14 days                                                                              3   3   3   1   1   1   3   1   4                                      __________________________________________________________________________     .sup.(1) Ext. X refers to Extender B, G, H, or I as appropriate for each      example.                                                                 

                  TABLE 4                                                         ______________________________________                                                  Example                                                                         8a      8b                                                        Components  (comp)  (comp)      8c   8d                                       ______________________________________                                        Polyether C 71.5    71.5        71.5 71.5                                     Extender A  --      8.75        13   17.5                                     Extender B  17.5    8.75        4.5  --                                       Equiv. ratio                                                                              --      1.0         0.35 0                                        Ext. B/Ext. A                                                                 Appearance                                                                    1 day       2       2           1    1                                        14 days     3       3           1    1                                        ______________________________________                                    

Cloud point tests

Cloud points were determined by warming the polyol blends with stirringat a rate of 2° C. per minute and recording the temperature at which theblends became clear. A phase-stable mixture has a cloud point below roomtemperature. Formulations and results are shown in Tables 5 and 6.Quantities are given in parts by weight.

                                      TABLE 5                                     __________________________________________________________________________           Example                                                                       9a  9b  9c          9f  9g  9h                                         Components                                                                           (comp)                                                                            (comp)                                                                            (comp)                                                                            9d  9e  (comp)                                                                            (comp)                                                                            (comp)                                     __________________________________________________________________________    Polyether A                                                                          71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                                                              71.5                                       Extender A                                                                           --  6   8.75                                                                              11.5                                                                              17.5                                                                              --  --  --                                         Extender B                                                                           17.5                                                                              11.5                                                                              8.75                                                                              6   --  --  --  --                                         Extender G                                                                           --  --  --  --  --  17.5                                                                              --  --                                         Extender H                                                                           --  --  --  --  --  --  17.5                                                                              --                                         Extender I                                                                           --  --  --  --  --  --  --  17.5                                       Equiv. ratio.sup.(1)                                                                 --  1.9 1.0 0.52                                                                              0   --  --  --                                         Ext. X/Ext. A                                                                 Cloud point                                                                          80  50  38  <19 <19 150 7   35                                         (°C.)                                                                  __________________________________________________________________________     .sup.(1) Ext. X refers to Extender B, G, H, or I as appropriate for each      example.                                                                 

                  TABLE 6                                                         ______________________________________                                                Example                                                                         10a      10b     10c                                                Components                                                                              (comp)   (comp)  (comp) 10d   10e                                   ______________________________________                                        Polyether C                                                                             71.5     71.5    71.5   71.5  71.5                                  Extender A                                                                              --       6       8.75   11.5  17.5                                  Extender B                                                                              17.5     11.5    8.75   6     --                                    Equiv. ratio                                                                            --       1.9     1.0    0.52  0                                     Ext. B/Ext. A                                                                 Cloud point                                                                             102      75      57     43    <19                                   (°C.)                                                                  ______________________________________                                    

The phase stability data in Tables 2-6 show that2-methyl-1,3-propanediol (i.e., extender A), whether used alone or mixedwith smaller amounts of other chain extenders, forms phase-stablemixtures with the isocyanate-reactive polyethers. The amount of theother chain extenders that can be blended with 2-methyl-1,3-propanedioland still form phase-stable mixtures is, however, somewhat dependent onthe composition of the polyether. For example, Example 10d shows that itmay be necessary to use smaller relative amounts of other chainextenders when using polyether C instead of polyether A. In general,however, phase-stable mixtures can contain up to about 0.6 equivalentsof such other chain extenders per equivalent of2-methyl-1,3-propanediol.

Propylene glycol (i.e, extender H) produced phase stable blends (seeTables 3 and 5) and acceptable adhesive performance (see Table 1) whenallowed to cure sufficiently. However, adhesives prepared usingpropylene glycol cure at a much slower rate than adhesives based on2-methyl-1,3-propanediol and are thus not recommended.

What is claimed is:
 1. A low-viscosity two-component filled polyurethaneadhesive having a urethane content of from 7 to 20 percent by weight,based on the weight of nonfilled polyurethane polymer, comprising(a) alow-viscosity isocyanate component in a quantity sufficient to providean isocyanate index of about 100 to about 150 comprising an organicpolyisocyanate wherein 0 to 10 equivalent percent of the isocyanategroups of said organic polyisocyanate have been modified by reactionwith one or more isocyanate-reactive compounds; and (b) a low-viscositycurative component that is resistant to phase separation comprising(i) 5to 50 equivalent percent, based on the total equivalents of amino andhydroxyl groups of component (b), of an isocyanate-reactive polyetherhaving an equivalent weight greater than 500 selected from the groupconsisting of polyether polyols, polyethers terminated by aromatic aminogroups, and mixtures thereof, (ii) 30 to 95 equivalent percent, based onthe total equivalents of amino and hydroxyl groups of component (b), of2-methyl-1,3-propanediol, and (iii) 0 to 35 equivalent percent, based onthe total equivalents of amino and hydroxyl groups of component (b), ofone or more chain extenders and/or crosslinkers other than2-methyl-1,3-propanediol having a molecular weight in the range 32 to400, with the proviso that the equivalent ratio of component (b)(iii) tocomponent (b)(ii) is no more than about 0.6,wherein at least one ofcomponents (a) or (b) contains at least one filler in a quantity of fromabout 10 to about 40 percent by weight based on the total quantity offilled polyurethane adhesive.
 2. A polyurethane adhesive according toclaim 1 wherein the organic polyisocyanate comprises a mixture ofdiphenylmethane-2,4'-diisocyanate and/ordiphenylmethane-4,4'-diisocyanate isomers, optionally in admixture withpolyphenyl polymethylene polyisocyanates, wherein the diphenylmethanediisocyanate isomers comprise from 20 to 100 percent by weight of thetotal organic polyisocyanate mixture.
 3. A polyurethane adhesiveaccording to claim 1 wherein the organic polyisocyanate is aurethane-modified and/or urea-modified MDI-based di- and/orpolyisocyanate in which no more than about 10 equivalent percent of theisocyanate groups have been modified by reaction with one or moreisocyanate-reactive hydroxyl- and/or amino-containing compounds having afunctionality of about 2 to about 6 and an equivalent weight greaterthan about
 500. 4. A polyurethane adhesive according to claim 1 whereinthe organic polyisocyanate is dicyclohexylmethane-2,4'-diisocyanateand/or dicyclohexylmethane-4,4'-diisocyanate.
 5. A polyurethane adhesiveaccording to claim 1 wherein component (b)(iii) comprises 0.5 to 35equivalent percent, based on the total equivalents of amino and hydroxylgroups of component (b), of one or more chain extenders and/orcrosslinkers other than 2-methyl-1,3-propanediol, wherein 0.5 to 20equivalent percent, based on the total equivalents of amino and hydroxylgroups of component (b), of said chain extenders and/or crosslinkers isa diamine and/or triamine.
 6. A polyurethane adhesive according to claim1 wherein component (b)(i) comprises 5 to 20 equivalent percent of thetotal equivalents of amino and hydroxyl groups of component (b),component (b)(ii) comprises 70 to 95 equivalent percent of the totalequivalents of amino and hydroxyl groups of component (b), and component(b)(iii) comprises 0.5 to 17 equivalent percent of the total equivalentsof amino and hydroxyl groups of component (b).
 7. A polyurethaneadhesive according to claim 1 wherein component (b)(i) is a polyetherpolyol, a PHD polyol, a polyether terminated with aromatic amino groups,or a mixture thereof.
 8. A polyurethane adhesive according to claim 7wherein the polyether polyol is a polyoxypropylene polyoxyethylene triolhaving an equivalent weight greater than
 500. 9. A polyurethane adhesiveaccording to claim 7 wherein the polyether terminated with aromaticamino groups is prepared by reacting a polyether containing two to fourhydroxyl groups with an excess of an aromatic polyisocyanate to form anisocyanate-terminated prepolymer and hydrolyzing saidisocyanate-terminated prepolymer to form the amine-terminated polyether.